In a wireless ad hoc network, each radio station exchanges routing information packets including routing information to a destination radio station with adjacent radio stations existing in a communicable range of the own station, and thus constructs a route from the own station to the destination radio station. For example, when a radio station constructs a plurality of routes to a destination radio station, the radio station selects a route with the lowest routing cost as an optimum route, and performs data transmission using the selected route. The above-mentioned routing cost is a total amount of link costs that are costs in accordance with radio quality of respective links on a route. However, in such a routing construction scheme, the route selection in consideration of traffic conditions is not performed. Thus, it is possible that traffic is concentrated at a certain radio station and the radio station becomes a bottleneck in the network. Moreover, in case of a tree-formed network, for example, traffic is concentrated at a certain radio station (radio station near the top).
Moreover, in the wireless ad hoc network, a radio station confirms a free state of a channel through carrier sense before performing data transmission. Then, when electric power higher than a given threshold is detected, the radio station determines that the channel is busy and does not perform data transmission. When electric power higher than a given threshold is not detected, the radio station determines that the channel is idle and starts data transmission. However, in the wireless ad hoc network, when a transmission radio station transmits data to a reception radio station as a destination at the same time as a radio station as a hidden node for the transmission radio station performs data transmission, data collision (a hidden node problem) occurs at the reception radio station. Thus, a transmission success rate deteriorates in the transmission radio station, and the communication capacity accordingly decreases. In particular, at the bottleneck radio station on a route constructed in the routing construction scheme described above, reception failure due to the hidden node problem occurs frequently, and the number of times of retransmission due to the reception failure increases, which further increases traffic. Thus, the communication capacity in the entire network decreases.
Meanwhile, a technique has been disclosed that allows routing construction avoiding a radio station where traffic is concentrated (a bottleneck radio station) in the routing construction scheme described above. To be more specific, each radio station calculates a link cost using a node cost in accordance with traffic conditions of the own station and a cost in accordance with radio quality of a link. Then, each radio station generates a routing cost to the own station by adding the link cost obtained from calculation to a routing cost in a received routing information packet, and transmits the routing information packet including the routing cost to adjacent radio stations. That is, each radio stations in the wireless ad hoc network exchanges routing information packets including the routing cost reflecting traffic conditions of the own station with adjacent radio stations. In this manner, the routing cost of a route including a bottleneck radio station becomes higher, and thus each radio station can perform routing construction avoiding a bottleneck radio station in the routing construction scheme described above.
Patent Document 1: Japanese Patent Application Laid-open No. 2005-303827
However, the conventional technique described above has a problem in which it is difficult to solve the above-mentioned hidden node problem when the bottleneck radio station is a destination radio station or a radio station that is inevitable on a route (radio station near the top of a tree-formed network, for example). That is, when it is impossible to construct a route avoiding a bottleneck radio station, reception failure due to the hidden node problem occurs frequently at the bottleneck radio station, and the number of times of retransmission increases due to the reception failure, which increases traffic. Thus, the communication capacity in the entire network decreases.